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Page 18 of 32 Yan et al. Energy Mater 2023;3:300002 https://dx.doi.org/10.20517/energymater.2022.60

Figure 7. (A) Schematic illustrations of Li deposition at various interfaces. Reprinted with permission from Ref. [125] . Copyright (2021)
Springer Nature. (B) Polyionic liquid coating on Li metal anode. Reprinted with permission from Ref. [132] . Copyright (2020) American
Chemical Society. (C) Stability comparison of PEO-coated Li and bare Li in water. Reprinted with permission from Ref. [133] . Copyright
(2020) Elsevier. (D) Schematic illustrations of mitigated surface concentration during concentration polarization with an artificial SEI
with a high dielectric constant. Reprinted with permission from Ref. [135] . Copyright (2021) American Chemical Society. (E) Schematic of
half-blocked coin cell before charging and after first charging. Reprinted with permission from Ref. [143] . Copyright (2018) National
+
Academy of Sciences. (F) MOF-based SSI formed on LMA with immobilized ionic channels for fast Li transport. Reprinted with
permission from Ref. [148] . Copyright (2020) Cell Press. (G) Uniform and stable ASEI on Cu. Reprinted with permission from Ref. [150] .
Copyright (2020) Springer Nature. (H) XPS depth profiles of Li 1s with three stages in regions I (red), II (green) and III (blue), with the
detection depth of XPS covering only the LiF layer, LiF+Li and Li, respectively. Reprinted with permission from Ref. [151] . Copyright (2017)
American Chemical Society.

Young’s modulus in α-PVDF are attributable to a dense microstructure and less porosity, which can
effectively promote a uniform Li deposition by decreasing the overpotential, lowering the local current
density and suppressing Li protrusions [Figure 7D] [135,136] . A flexible Young’s modulus (1-0 GPa) for an ASEI
can be achieved with semi-crystalline and crystalline polymers that can increase the strength of the
backbone. In contrast, inorganics, such as ceramics, generally provide a high Young’s modulus
(10-100 GPa), which enables resistance to the stress imposed by the growing dendrites (4.2 GPa).
Furthermore, Li-ion conductive inorganics, like Li N , LiF , Li S and Li PO 4 [140] , as well as passive
[139]
[138]
[137]
3
3
2
inorganics that solely impart mechanical stiffness at the interface, like Al O 3 [141] and nano-diamond
2
coatings , are considered as high mechanical modulus candidates.
[142]
The heterogeneous transport of Li ions in the native SEI is due to differences in diffusion rates in different
+
regions, which is the main triggering factor of dendrites. Maintaining fast and uniform Li-ion flux is critical
to suppressing the formation of dendrites. Shi et al. revealed the stripping mechanism on a Li anode by
[143]
visualizing the interface between the stripped Li and the SEI [Figure 7E] . After the cations migrate
through the SEI layer, the metal vacancies will be left on the Li electrode below the SEI layer. The
aggregation of metal vacancies can lead to the formation of large cavities at the Li/SEI interface, which is
fatal for the adherence of the SEI layer. Tewari et al. revealed that ion depletion easily resulted in a scarcity